CV

Professional experience

Post-doc

Modelization of plasticity in reinforced rubbers.
Remplacing carbon black by silica in the tread of tires allowed for decreasing the rolling resistance, while preserving good grip properties (green tires). Improving this grip-rolling resistance trade-off is a major industrial challenge, which requires to understand the role of fillers (silica, carbon black) in the mechanical behavior of reinforced rubbers.
But the polymer dynamics is modified in the vicinity of a solid interface like a filler: the glass transition temperature Tg locally increases, which leads to the formation of glassy bridges between the filler particles. Polymer dynamics close to solid substrates is a very active research topic, as fundamental science concerning glass transition in thin films (theory and experiments) and from an applied perspective as regards consequences on the mechanical properties of nanocomposites.
The model of Long et al. of glass transition, based on the role of dynamical heterogeneities, gives an interpretation of Tg shifts close to a solid substrate. I developed a mesoscopic description of the polymer confined between two substrates, allowing for implementing the physical concepts of this model in numerical simulations of the mechanics. We obtain that at great deformation, two plasticity mechanisms can occur (flow or desorption) depending on the system under study (filler-polymer interaction) and on the operating conditions (frequency, temperature). In the elastic regime, Tg shifts are obtained with the film thinness for the first time in simulations of the mechanical response.
Reference : Europhys. Lett.103 (2013) 26002.

PhD

Laboratory of Physics of the École Normale Supérieure of Lyon, 2005 — 2008

Lehmann effects in liquid crystals
Cholesteric liquid crystals generally have a helical structure due to the presence of chiral molecules. In these systems a linear thermomechanical coupling can be observed, the Lehmann effect: a temperature gradient exerts a torque on the local orientation of the molecules. The explanation of this coupling by Leslie appeals to a phenomenological coefficient ν which can only be non-zero in chiral phases.
On the other hand, there are cholesteric called compensated, the structure of which spontaneously unwinds at a particular temperature, leading to an achiral structure. In this PhD work, we have experimentally shown that ν does not vanish at the unwinding temperature. This implies that the phase is still chiral at this temperature, a point which was up to then controversial. The order of magnitude of Leslie’s coefficient ν was estimated from new experiments made using static deformations or continuous rotations of the cholesteric texture.
Reference : Effet Lehmann dans les cristaux liquides cholestériques (École Normale Supérieure de Lyon, 2008)

Instructorship

CIES de Lyon, 2005 — 2008

During my PhD, I teached at the École Normale Sup’ Lyon to students preparing the competitive exam of the highest French teaching degree in physics (and chemistry). Annual duty: 64 h :

Corrections of lessons et practical works

Supervision of practical works (optics, magnetism, mechanics)

Exam subject based on knowledge in physics about optics of non-linear, heterogeneous or anisotropic materials.